B3 -Living and Growing

DNA = a double helix made up of the complimentary base pairings A and T, C and G.

Ribosomes are found in the cytoplasm and are where protein synthesis takes place.

Protein Synthesis = the process of turning amino acids into proteins.

-The cross links holding the base pairs together unravel

-A copy of each base is made using its complimentary pairing

-These copies are taken out of the nucleus to the ribosomes by mRNA

-The base sequence in the DNA code for different amino acids

-Different series of amino acids code for different proteins

Proteins are made up of long chains of amino acids.

-Structural proteins are used to build cells and tissues eg. collagen

-Hormones carry messages to control reactions eg. insulin

-Enzymes act as a biological catalyst

-Carrier proteins eg. haemoglobin to carry oxygen

Enzymes speed up reactions in the body in a process known as the 'lock and key' process

Enzymes can be affected by pH and temperature.

At low temperatures, enzymes move slowly so successful enzyme-substrate collisions are less likely.

At very high/low pH levels enzymes denature.

Mutations occur through either spontaneous changes in DNA sequencing, or radiation. They can be harmful, or harmless and sometimes have no effect. Occasionally, they can be advantageous to the individual.

Every cell has the same genes, but some genes are switched off in different cells so they can perform different functions.

Gene mutations alter or prevent the production of the proteins that are normally made.

Respiration releases energy from food, which is trapped in a molecule called ATP.

Aerobic respiration = when oxygen is involved.

C₆H₁₂O₆ + 6O₂    →    6CO₂ + 6H₂O (+ energy)

Anaerobic respiration =the breaking down of glucose into lactic acid and energy.

Anaerobic respiration takes place when there is an insufficient supply of oxygen. The lactic acid build up (oxygen debt) in the muscles causes pain and fatigue.

The breathing and heart rates remain high during recovery to carry the lactic acid to the liver and break it down.

Respiratory Quotient = CO2 produced/O₂ used

Mitosis creates two genetically identical cells.

Meiosis creates four haploid cells, all genetically different.

Plasma = the liquid part of the blood. It carries important substances around the body:

- Digested food substances (eg. glucose)

- Carbon Dioxide (from the tissue to the lungs)

- Hormones (from the glands to the target cells)

- Plasma proteins (eg. antibodies)

- Waste substances (eg. urea)

Red blood cells:

- Small, to fit through blood vessels

- Biconcave, to increase surface area and make oxygen exchange quicker

- Contain no nuclues, so more haemoglobin fits in the cell

The haemoglobin in the red blood cells combines with the oxygen to form oxyhaemoglobin. When oxyhaemoglobin reaches the tissues, the oxygen is released.

The stages of human growth are: infancy, childhood, adolescence, maturity and old age.

Measuring growth in terms of length is easy, but only measures growth in one direction. Measuring wet mass is hard for some organisms such as trees, but is easier for animals. Dry mass measures the true growth of organisms, but can only be measured by killing the organism.

Most animals grow up to a certain size, but plants continue growing. Plant cell division happens in areas called meristems in the root and tip.

Stem cells are undifferentiated, so can develop into different types of cells and they could potentially be used to treat some medical conditions.

There are some moral issues surrounding stem cell research, due to them being found mainly in embryos. In order to get the stem cells, the embryos are distroyed. 

Selective breeding can lead to health problems as a result of inbreeding and the reduction of the gene pool. It also means there is a reduction in variation, so populations are not able to adapt as easily.

The process of genetic engineering:

- Desired characteristics are selected

- Responsible genes are located and isolated

- These genes are inserted into other organisms

- Organisms are allowed to reproduce

Gene therapy uses genetic engineering to change genes or cure certain disorders.

Gene therapy in gametes is controversial, because it could lead to 'designer babies'.

Plants can be cloned through tissue culture. Small tissue samples are cut from a selected plant and grown in test tubes or dishes containing a growth medium. Aseptic technique is used to stop cross-contamination.